Fast Frequency-Tunable External-Cavity Laser.

This paper describes a tunable, narrow line, external cavity laser that can be frequency-shift keyed (FSK) up to 100 Mb/s by modulating the laser current. The fast frequency modulation capability is achieved by using a laser chip having a two-section contact. One section is biased at a constant current to generate the optical signal; the other section, biased below threshold, acts as an optical waveguide with a bias-controlled variable refractive index. This two-section laser yields a frequency deviation of 50 MHz/mA with an optical power of 3 dBm at 1. 3microns. Such a laser provides simultaneously the high spectral purity, large tuning range and frequency modulation capability needed for demonstration of a coherent optical multi-user network using Wavelength Division Multiplex (WDM) and FSK modulation.